chore: add test bootstrap, update phpunit config, and add Laravel 13 support to README

- Add tests/bootstrap.php to suppress PHP 8.4 vendor deprecation notices (Mockery implicit-nullable)
- Update phpunit.xml.dist to reference bootstrap, use PHPUnit 11.5 schema, and ignore indirect deprecations
- Note Laravel 13 support in README

tests/bootstrap.php

@@ -0,0 +1,14 @@
+<?php
+
+require __DIR__ . '/../vendor/autoload.php';
+
+// Suppress PHP 8.4 deprecation notices that originate from vendor code.
+// These are typically from third-party packages (e.g. Mockery) that have not
+// yet updated implicit-nullable parameter signatures and are not actionable here.
+set_error_handler(static function (int $errno, string $errstr, string $errfile): bool {
+    if ($errno === E_DEPRECATED && str_contains($errfile, DIRECTORY_SEPARATOR . 'vendor' . DIRECTORY_SEPARATOR)) {
+        return true;
+    }
+
+    return false;
+}, E_DEPRECATED);